1. Technical Field
The present disclosure is related generally to methods and systems for moving fluids, more particularly, methods and systems for generating fluid flow that increases fluid exposure to an energy source for sterilization or disinfection.
2. Related Art
Water use is a major environmental concern and methods to reduce and reuse water consumption are in demand. In food processing facilities, water shortages have made water reclamation and reuse an integral component of environmental programs. To ensure that re-used effluents do not pose an unreasonable risk to public health, the Environmental Protection Agency (EPA) has outlined strict regulations for water reclamation. These water disinfection regulations provide a substantial public health benefit by reducing discharges of many waterborne pathogenic organisms to water supplies, recreational water, shellfish water and other waters that can potentially transmit disease to humans.
Many technologies exist for bacterial destruction in water reclamation such as chlorination which is a relatively low cost disinfection process. Chlorine treatment, however, presents a number of problems. For example, chlorine disinfection is incapable of achieving appreciable inactivation of the several viruses and protozoa, specifically, Cryptosporidium parvum at reasonable disinfectant doses and contact times (Sobsey, M. D. (1989). Inactivation of health-related microorganisms in water by disinfection processes. Wat Sci. Tech. 21:179-195). In addition, large chlorine concentrations generate chloro-organic, disinfection by-products such as trihalomethanes (THMs) and other carcinogens that persist in the environment (Matsunaga, T., and M. Qkochi. (1995). TiO2-Mediated Photochemical Disinfection of Escherichia coli Using Optical Fiber. Environ. Sci. Technol. 29:501-505).
Due to the environmental concerns associated with chemical disinfection, current water treatment methods are moving away from traditional chemical to physical procedures (Cho, I. H. et al. (2002). Disinfection effects E. coli using TiO2 AJV and solar light system. Wat. Sci. and Tech. 2: 181-190). For example, use of ultraviolet (UV) radiation is becoming more popular for wastewater treatment since it is effective against both bacteria and viruses, leaves no residues and is economical (Wong, E. et al. (1998). Reduction of Escherichia coli and Salmonella senftenberg on pork skin and pork muscle using ultraviolet light. Food Microbiology. 15:415-423). UV processing uses radiation in the germicidal range from 200 to 280 nm to generate DNA mutations within pathogens (Federal Department of Agriculture and Center for Food Safety and Applied Nutrition. (2000). Kinetics of microbial inactivation for alternative food processing technologies. Ultra-violet light). The latter study also concludes that to achieve microbial inactivation, the UV radiant exposure must be at least 400 J/m2 in all parts of the product. Moreover, UV irradiation is particularly effective when it is used in conjunction with powerful oxidizing agents such as ozone and hydrogen peroxide.
Treatment of fluid flow is also important in food processing for example in processing of beverages such as milk, juices, alcoholic drinks or soft drinks. Existing methods for treating fluid foodstuffs typically include exposing the foodstuffs to high temperatures in an effort to neutralize potentially harmful bacteria. Unfortunately, thermal treatment of foodstuff can cause the breakdown of ingredients including proteins and vitamins. The United States Food and Drug Administration (US-FDA) has recently published a ruling (21 CFR 179) that approves the use of UV radiation in place of pasteurization.
Early modeling of disinfection efficiencies in flow-through UV reactors focused on the ideal designs of either a completely mixed (stirred tank) or plug flow configurations (Haas, C. N. and Sakellaropoulos, G. P. (1979). Rational analysis of ultraviolet disinfection reactors, Proceedings of the National Conference on Environmental Engineering, American Society of Civil Engineering, Washington, D.C.; Severin, B. F. et al. (1984) Kinetic modeling of UV disinfection of water. Inactivation kinetics in a flow-through UV reactor, J WPCF. 56:164-169). As summarized by the Water Environment Federation (Water Environment Federation (1996). Wastewater Disinfection Manual of Practice FD-10, chapter 7, Alexander, Va.), Scheible (Scheible, O. K. (1987). Development of a rationally based design protocol for the ultraviolet disinfection process. J. Water Pollution Control Fed. 59:25-31) developed a model to account for non-ideal reactor theory that requires four empirical constants. A strictly empirical model was also proposed by Emerick and Darby (Emerick, R. W. and Darby J. L. (1993). Ultraviolet light disinfection of secondary effluents: predicting performance based on water quality parameters. Proc. Plann. Des. and Oper. Effluent Disinfection Syst. Spec. Conf., Water Environment Federation, Whippany, N.J., p. 187) to account for a number of factors that influence water quality. Recently, computational fluid dynamic (CFD) solutions have provided insight into the turbulent flow characteristics of UV reactors (Lyn, D. A. et al. in E.R. (1999). Numerical Modeling of flow and disinfection in UV disinfection channels, J Environ. Eng. 125, 17-26).
Of the two ideal designs and considering a single reaction, it is well established that plug flow provides comparable yield but with a substantial reduction in holdup volume that can exceed two orders of magnitude compared to a completely mixed reactor (Levenspiel, O. (1972). Chemical Reaction Engineering, 2nd Ed., John Wiley and Sons, Inc., New York, N.Y.). For such plug flow designs, the surface-to-volume ratio is large which is favorable to the transmission of UV radiation through the reactor walls and contained fluid. The major limitations to plug flow designs, however, are both non-uniform radiation intensities within the fluid and low concentrations of absorbing species such as viable pathogens near irradiated walls. The effects of the latter are reduced by increasing the flow rate thus reducing the velocity and concentration boundary layer thickness but, unfortunately, also the residence time and thus the radiation dosage.
Previous studies on the effects of radiation in Taylor-Couette flow are the growth of algae (Miller, R. L. et al. (1964). Hydromechanical method to increase efficiency of algal photosynthesis, Ind. Engng. Chem. Process Des. Dev. 3:134) and the development of a reactor for heterogeneous photocatalysis (Sczechowski, J. G. et al. (1995). A Taylor vortex reactor for heterogeneous photocatalysis, Chem. Eng. Sci. 50:3163).
Recently, the inventors herein (Forney, L. J., and Pierson J. A., (2003), Optimum photolysis in Taylor-Couette flow, AIChE 1.49:727-733; Forney, L. J. and Pierson, J. A. (2003), Photolylic reactors: similitude in Taylor-Couette and channel flows, AIChE J. 49:1285-1292, both of which are incorporated by reference in their entirety as if fully set forth herein) considered a fast photolytic reaction and demonstrated that optimum photoefficiencies could be achieved if the radiation penetration depth were controlled in relation to the velocity, boundary layer thickness. Their latter work also provided a scaling law for the yield in both Taylor-Couette and channel flows.
Thus, there is a need for systems and methods for the non-thermal processing of fluids.
There is another need for systems and methods for the non-thermal control of micro-organisms in edible fluids.